This invention relates to apparatus for the aseptic packaging of high acid food products. More specifically, the present invention is directed to novel apparatus for carrying out a method whereby pre-formed oxygen and water vapor barrier plastic containers are sprayed with and immersed in an aqueous sterilizing bath at a temperature ranging from 212.degree. F. to 140.degree. F. for a time interval ranging from less than 1 second to 3.5 minutes, following which, after draining the sterilizing liquid therefrom, the containers are filled with pre-sterilized high acid food product in a sterile inert gas environment at or above atmospheric pressure and thereafter closed in the same sterile inert environment by sealing a dry sterile closure element thereto.
Although packaging of high acid food products for ambient temperature storage and distribution has been conducted in glass bottles and metal cans for many years, costs of these containers, their closures and labels have increased rapidly and are projected to continue to rise. Cost of thermoplastic materials has not increased as rapidly and are projected to increase at a lower rate than metal or glass. Further, these materials are more conserving of energy on a packaging and distribution systems basis. Therefore, packaging in thermoplastic materials represents a significant saving in packaging costs. Most packaging thermoplastics are oxygen permeable, and food packaging in such materials leads to higher cost of refrigerated distribution methods. Further, because of the heat sensitivity of most thermoplastics, conventional hot filling and terminal thermal sterilization techniques used commercially for cans or glass damage or destroy most thermoplastic packages capable of containing products under ambient conditions for prolonged periods. On the other hand, application of aseptic techniques would permit commercial sterilization of the packages under controlled conditions which leave the package unaltered and undamaged. As a further advantage of aseptic packaging, the product may be heated and cooled to achieve commercial sterilization outside of the package and thus very rapidly prior to packaging, and so is minimally altered by processing. A higher quality product results from the practice of this invention.
The high acid food products contemplated are those juices, fruits, vegetables and products having a pH of less than 4.6. Included are fruit juices, fruit juice drinks, fruit flavored drinks, nectars, jams, jellies, fruit syrups, catsup, tomato juice, tomato puree, tomato sauce, gelatin desserts, sauces and purees in fluid or semifluid form, and similar low pH dairy products such as fermented milk products, buttermilk, fresh cheese and yoghurt. Also contemplated are food products with a water activity greater than 0.85 and pH less than 4.6, such as whole, sliced and diced fruit, tomato products and formulated food products.
Aseptic packaging is employed for food products in order to permit a lower thermal input to achieve commercial sterilization and thus permit significantly higher quality products; to permit the use of packaging materials sensitive to heat; and to allow the filling of product into large containers which would otherwise require hours or days to cool. Aseptic packaging as used herein comprises commercial sterilization of food or other products external to and independently of the packaging; separate commercial sterilization of the packaging material; bringing them together in a commercially sterile environment; and hermetically closing them in a commercially sterile environment.
Because no terminal sterilization process is available to compensate for any errors or deviations in microbiological loading, viscosity, etc., every unit operation and unit of apparatus must be precise. Any casual application of equipment represents a potential entry access for microorganisms or air, both of which violate the integrity of the product. Further, aseptic packaging apparatus must be simple and not prone to interruption or breakdown, since any repair would require breaking seal integrity. All apparatus components must function at a high degree of reliability, permitting no entry of microorganisms or air, with no breakdown. All apparatus must remain functional while retaining commercial sterility.
Sterilization in the strict definition is an absolute: the absence of all microorganisms. Foods and analogous products are generally not sterile in the absolute sense. Rather, they are commercially sterile, a concept employed throughout industry and acceptable to regulatory authorities. Commercial sterility is the absence of microorganisms of public health significance and the absence of microorganisms capable of causing spoilage under normal conditions of distribution.
Aseptic and other packaging of most high acid products for ambient temperature distribution employs commercial sterilization procedures. Most high acid fluid food products are also highly sensitive to oxygen dissolved in the product and in the head space of packages. Hot filling used for most canning and bottling permits the presence of head space oxygen.
Commercial cold filling of high acid products makes no provision for removal of oxygen in the head space and generally obviates the problem by refrigerated distribution which reduces the rate of biochemical interaction of oxygen and product.
Chilled juice and other high acid packaged products minimize the problems of both microbial and oxygen presence by low temperature distribution which reduces the rate of microbiological propogation and the rate of biochemical reaction of oxygen and product.
In accordance with the present invention, the high acid food product is processed into the form (e.g. juice, sauce, puree, etc.) to be packaged, and is commercially sterilized prior and external to packaging by suitable means, as by heating. Thus the food product delivered to the aseptic packaging operation is essentially free of spoilage microorganisms, i.e., commercially sterile. The pre-formed plastic containers into which the commercially sterile food product is to be packaged require commercial sterilization before the food is placed therein.
Containers and their closures may be fabricated at a location remote from the food processing/packaging operation. While fabrication thereof is conducted under conditions of good manufacturing practice, opportunities exist for the contamination thereof by undesirable microorganisms which could cause spoilage of food packaged therein. Thus, the apparatus has the capability of commercially sterilizing the containers and their closures.
Another essential element of this invention is the reduction of oxygen virtually to extinction in the interior of the package, and the subsequent retention of the oxygen level to well below 1% of the head space volume in the sealed package. High acid food products such as fruits, fruit products and tomato products are susceptible to rapid loss of vitamin C, flavor and color by exposure to oxygen. In conventional canning practice for high acid food products, product is heated and filled hot prior to closure. For some products, a short high-temperature holding time is required. Cooling is required to arrest overcooking once the sterilization value has been achieved. Upon cooling, a partial vacuum of up to 22 in. Hg is effected through condensation of head space steam arising from the product. Products contained in cans and bottles thus packaged undergo oxidative biochemical changes due to the presence of occluded and dissolved oxygen in the product and of residual oxygen in the head space. The quantities of oxygen present in conventional practice are sufficient to oxidize the vitamin C naturally present, flavors and colors, and to render the product suboptimal and even unacceptable. To reduce the oxygen dissolved and occluded in the product, it is preferred that the product be treated as by centrifugation or vacuum prior to packaging.
The present invention requires that the filling and closing of the barrier plastic containers be conducted in an inert atmosphere such as sterile nitrogen to ensure that head space oxygen content after sealing is well below 1% by volume. By conducting the entire filling and closing operation in the absence of oxygen, a head space inert atmosphere is assured. Alternative conventional methods such as vacuum evacuation and replacement, or direct displacement by pressurized inert gas, both disturb the surface and do not ensure the absence of oxygen in the package. Further, this invention mandates that the packaging materials be composed of oxygen and water vapor barrier materials to minimize the quantity of oxygen and water vapor which can migrate through the walls of the package after closure.